1. Field of the Invention
The present invention relates to a polymer suitable as a base resin for a positive resist composition, especially for a chemically amplified resist composition, a positive resist composition using the same, a patterning process, and a polymerizable compound to obtain the polymer thereof.
2. Description of the Related Art
As LSI progresses toward a high integration and a further acceleration in speed, a finer pattern rule is rapidly progressing. In particular, the expansion of a flash memory market and the enlargement of a memory capacity lead the finer pattern rule. Mass production of a 65-nanometers node device by a miniaturized fine line of an ArF lithography is currently in practice and preparation of the mass production of a 45-nanometers node device by a next generation ArF-immersion lithography is now progressing. As the candidates for the post next generation technology, a 32-nanometers node, an immersion lithography by a ultra high NA lens comprising a liquid having a higher refractive index than water, a high-refractive lens and a high-refractive resist, an extreme ultraviolet (EUV) lithography of 13.5-nanometers wavelength, and a double exposure (a double patterning lithography) of an ArF lithography, and the like are being studied.
In a high energy beam of an extremely short wavelength such as an EB (an electronic beam) and an X-ray, a light element such as a hydrocarbon used in a resist has almost no absorption, and thus a resist composition based on polyhydorxystyrene has been studied.
An EB resist has been practically used for a mask drawing. In recent years, a mask production technology has been considered to be a problem. A reduced projection exposure system with a one-fifth reduction ratio had been used from the time of a g-beam exposure, but an effect of the size misalignment of a mask on a size change of a pattern on a wafer becomes a problem because an enlarged chip size, a projection lens with an enlarged diameter, and also a one-fourth reduction ratio have been employed. In addition, as the pattern miniaturization progresses, it is pointed out that a size misalignment on a wafer is becoming larger than a size misalignment of a mask. A Mask Error Enhancement Factor (MEEF) is calculated by using a mask size change as a denominator and a size change on a wafer as a numerator. In the pattern of a 45-nanometers class, it is not a rare case that MEEF is 4 or more. If the reduction ratio is one-fourth and MEEF is 4, it can be said that the precision equivalent to that of a substantially same magnitude mask is necessary in the mask production.
To improve a precision of a line width in a mask production, exposure instruments using a laser beam to an electronic beam (EB) have been used. In addition, because a further miniaturization becomes possible by raising an acceleration voltage of an electron gun, a voltage of 10 to 30 keV, and of 50 keV becomes a mainstream recently, and the study is progressing toward 100 keV further.
Here, as an increase in the acceleration voltage, a tendency to a lower sensitivity of a resist becomes a problem. A higher acceleration voltage enables to improve a degree of resolution and a size controlling because the effect of a front scattering in a resist film becomes smaller, leading to an improvement in a contrast of an electronic drawing energy, but a sensitivity of a resist is decreased because an electron passes through a resist film freely. Because a mask exposure instrument exposes a light directly for drawing with one stroke, a decrease in the resist sensitivity leads to a decrease in productivity and thus is not desirable. In view of a request for a higher sensitivity, a chemically amplified resist is being studied.
As a miniaturization of a pattern of an EB lithography for a mask production progresses, a move to a thinner resist is progressing in order to prevent a pattern fall due to a high aspect ratio at the time of development from occurring. In the case of a optical lithography, the move to a thinner resist contributes greatly to an improvement in the resolution. This is owing to a progress in flattening of a device by introduction of a CMP and the like. In the mask production, a substrate is flat, thus a film thickness of the substrate to be processed (for instance, Cr, MoSi and SiO2) is determined by the light shielding rate and the phase difference control. In order to make it thinner, an improvement in a dry-etching resistance of a resist is necessary.
Meanwhile, it is generally assumed that there is a relationship between a resist carbon density and a dry-etching resistance. In the EB drawing not affected by an absorption, a resist based on a novolak polymer having a good etching resistance has been developed.
In addition, it is reported that an absorption of a carbon atom is small in a soft X-ray (EUV) exposure using a 5-20 nanometers wavelength which is expected, along with an F2 exposure, as a promising exposure method in a fine processing using a 70 nanometers wavelength or in a process that follows thereafter. A higher carbon density is effective not only for improvement in the dry-etching resistance but also for increase in a transmittance in the region of a soft X-ray wavelength (N. Matsuzawa et al., Jpn. J. Appl. Phys. Vol. 38, p 7109-7113 (1999)).
As a miniaturization of the patterning processing progresses, an indistinct image due to diffusion of an acid became a problem (SPIE Vol. 5039, p 1 (2003)). To secure the degree of resolution in a fine pattern in the post 45 nanometers size, it is proposed that not only an improvement in the dissolution contrast, which has been proposed in the past, but also a suppression of diffusion of an acid are important (SPIE Vol. 6520, 65203L-1 (2007)). However, in a chemically amplified resist, there has been a problem in that a sensitivity and a contrast are markedly decreased if diffusion of an acid is suppressed to the maximum extent by lowering the temperature of a post exposure bake (PEB) and shortening the time of a PEB, because a sensitivity and a contrast are increased by diffusion of an acid.